1. Field of the Invention
The present invention relates to the measurement of magnetic effects due to eddy currents, but more specifically, the present invention relates to a discrete-time method of measuring the magnetic effects due to eddy currents induced into conductive material by sinusoidally time-varying magnetic fields.
2. Description of the Prior Art
Magnetic effects due to eddy currents can be measured by applying a large sinusoidally varying magnetic field to the conductive material being measured. This applied field induces an alternating current in the conductive material which in turn induces an alternating magnetic field that is ninety degrees out of phase with the applied field and at the same frequency.
A previous method used to measure eddy current effects required cancellation of the applied field by using an analog signal to drive a "compensation coil" wound around the measurement magnetometer. This signal was derived from the current being used to produce the applied field and passed through a "compensation circuit" consisting of an amplifier and phase shifter. The amplitude and phase of the compensation signal were manually adjusted so as to cancel the applied field at the measurement magnetometer.
In test facilities where it is desired to use over one hundred measurement sensors, for example, the manual adjustment of all compensation circuits becomes a difficult and time-consuming task. In addition, variation in the values of analog components of the compensation circuit due to temperature and aging cause a loss of applied field cancellation, requiring that all compensation circuits be adjusted before every test.